1. Field of the Invention.
This invention relates to alcohol ethoxlates which have a low residual ethylene oxide or propylene oxide content. 2. Statement of Related Art.
Surface-active alkyl polyglycol ethers from the reaction of relatively long chain alcohols with ethylene oxide and/or propylene oxide have been known for decades. They are important representatives of the class of nonionic surfactants. Wetting or emulsifying auxiliaries of similar structure are obtained by ethoxylation of comparable components containing free hydroxyl groups while low-foam surfactants are obtained by addition of propylene oxide and, optionally, ethylene oxide onto such components. Partial derivatives of polyhydric alcohols with relatively long chain reactants are mentioned as examples. Typical examples are partial esters of such polyhydric alcohols with relatively long-chain carboxylic acids, for example with fatty acids of natural and/or synthetic origin. Starting materials of this type, for example corresponding glycerol partial esters or sorbitan partial esters, are also converted by ethoxylation/propoxylation into corresponding reaction products containing polyglycol ether groups which have wetting and/or emulsifying or low-foam properties and which are widely used in cosmetics, in the textile field, particularly in the washing of textiles, and/or generally in the home and in industry.
The ethoxylation or propoxylation of such alcohol functions is carried out at elevated temperature and pressure in the presence of acidic or basic catalysts. The use of basic compounds of the alkali metals is of particular significance in this regard in all those cases where the starting compounds to be ethoxylated show a substantially neutral reaction. Such basic catalysts include, primarily, sodium and/or potassium alkoxylates, such as sodium or potassium methylate or the corresponding ethylates. Other commonly used basic alkali metal catalysts are sodium and potassium hydroxide.
In addition to satisfying the reqirements which active surfactants in general have to meet, a certain characteristic of these auxiliaries has recently been receiving increasing attention in regard to the use of the above-mentioned nonionic surfactants in practice, namely their residual content of unreacted ethylene oxide. Thus, according to a recommendation of the Bundesgesundheitsamt der Bundesrepublik Deutschland (Federal Health Office of the Federal Republic of Germany), cf. Bundesgesundheitsblatt 29 (1986), pages 21, 22, the content of free EO in the nonionic surfactant should not exceed a limit of 1 ppm if the application envisaged for the compounds in question here involves close contact with the body. To establish residual EO contents as low as these, additional purification measures were necessary for the ethoxylation processes hitherto practised on an industrial scale using alkaline catalysts. Thus, according to Applicant's earlier German patent application P 37 08 813 (D 7844), the residual content of free EO in the ethoxylation product is reduced to the necessary levels by treatment with steam.
The same concerns apply to propoxylation where it is also desired to obtain propoxylates having the lowest possible residual contents of free PO.